1. Field of the Invention
This invention relates to a receiving device and a signal receiving method, and more particularly, is applicable to a wireless communication system such as a portable telephone system.
2. Description of the Related Art
In this kind of wireless communication system, an area for offering the communication service is divided into cells with the desired size and a base station is provided in each cell as the fixed wireless station respectively, and portable telephone equipment as the mobile wireless station is arranged to wireless-communicate with the base station in the cell in which the portable telephone equipment itself exists. Although various types of communication systems have been proposed, one of typical devices is a time division multiple access system called the TDMA system.
This TDMA system is a system to divide the predetermined frequency channel into frames of the fixed time width F0, F1, . . . , as shown in FIGS. 1A and 1B and further divides the frame into time slots of the fixed time width TS0 to TS3 respectively, and users transmit the transmission signal when the time slot TS0 is allocated to his own station using a common frequency channel, and this system has made possible the realization of multiple communications (i.e., multiplex communications), users share a common frequency and frequency can be utilized efficiently. Thereinafter the time slot TS0 allocated to transmission is referred to as transmission slot TX, and the data block to be transmitted by one transmission slot TX is referred to as slot.
At this point, the transmitting device and receiving device of the wireless communication system for transmitting and receiving the digital signal using this TDMA system will be described referring to FIGS. 2A, 2B, 3A and 3B. In this connection, the transmitting device and the receiving device shown in FIGS. 2A, 2B, 3A and 3B are loaded on the portable telephone equipment and the base station of the portable telephone system, and are used for the communication from the portable telephone equipment to the base station or the base station to the portable telephone equipment.
As shown in FIG. 2A, the transmitting device 1 is roughly comprised of a convolutional coding circuit 2, an interleave buffer 3, a slotting processing circuit 4, a differential quadrature phase shift keying (DQPSK) modulation circuit 5, a transmission circuit 6 and an antenna 7, and first, inputs the transmission data S1 to be transmitted to the convolutional coding circuit 2.
The convolutional coding circuit 2 is comprised of a register and exclusive OR circuit of the fixed number of stages, and it applies convolutional coding to the input transmission data S1 and outputs the resultant transmission symbol S2 to the interleave buffer 3. The interleave buffer 3 sequentially stores the transmission symbol S2 in the memory area in order, and when the transmission symbol S2 is stored in said whole memory area (i.e., the desired volumes of transmission symbol S2 is stored), it permutes the transmission symbols S2 in random order (hereinafter this permutation is referred to as interleave) and outputs the resultant transmission symbol S3 to the slotting processing circuit 4. In this connection, the interleave buffer 3 has the memory capacity for multiple slots so that the transmission symbols can be spread out over a large number of transmission slots TX.
The slotting processing circuit 4 divides said transmission symbol S3 into slots in order to allocate the transmission symbol S3 to the transmission slots TX and sequentially outputs the transmission symbols S4 slotted to the DQPSK modulation circuit 5 per slot. The DQPSK modulation unit 5, by applying the DQPSK modulation processing to the transmission symbol S4 to be supplied per slot, forms a transmission signal S5 of which the symbol information is shown by the phase value and outputs this to the transmission circuit 6.
The transmission circuit 6, after applying the filtering processing to the transmission signal S5 to be supplied per slot, converts said transmission signal S5 to the analog signal, and forms the transmission signal with the fixed frequency channel by applying the frequency conversion onto the analog transmission signal, and after amplifying this to the fixed power, transmits this via an antenna 7. Thus, the transmission signal S6 divided into slots is transmitted from the transmitting device 1 synchronizing with the timing of transmission slots TX. In this connection, for reference purposes, a brief diagrammatic sketch of the signal processing to be conducted in each circuit of the transmitting device 1 described above is shown in FIG. 2B.
On the other hand, as shown in FIG. 3A, the receiving device 10 is roughly comprised of an antenna 11, a receiver circuit 12, a DQPSK demodulation circuit 13, a slot connecting processing circuit 14, a deinterleave buffer 15 and a Viterbi decoding circuit 16, and receives the transmission signal S6 transmitted from the transmitting device 1 by the antenna 11 and inputs this to the receiving circuit 12 as the received signal S11. The receiver circuit 12, after amplifying the input signal received S11, takes out a baseband signal by applying frequency conversion to said received signal S11 and after applying the filtering processing to this baseband signal S11, takes out received signal S12 which is DQPSK modulated by converting the baseband signal to the digital signal, and outputs this to the DQPSK demodulation circuit 13.
The DQPSK demodulation circuit 13 takes out symbol information by applying the DQPSK demodulation processing to the received signal S12 and outputs this to the slot connecting processing circuit 14 as a received symbol S13. In this connection, the value of this received symbol S13 is not binary signal such as xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d but it is a multi-level signal since noise element has been added on the transmission route. The slot connecting processing circuit 14 is a circuit to connect the received symbol S13 to be obtained fragmentally on a slot-by-slot basis to become continuous signal, and when the received symbol S13 is stored for the memory capacity of the deinterleave buffer 15 of the later stage, connects said received symbol S13 and outputs the connected received symbol S14 to the deinterleave buffer 15.
The deinterleave buffer 15 has a memory capacity for multiple slots, and after successively storing the received symbol S14 to be fed to the internal memory area, returns the received symbol S14 to the former order by permuting said received symbol S14 with the procedure contrary to the procedure conducted in the interleave buffer 3 of the transmitting device 1 and outputs the resulting received symbol S15 to the Viterbi decoding circuit 16 (hereinafter the procedure returning to the former order is referred to as deinterleave). The Viterbi decoding circuit 16 is comprised of a soft-decision Viterbi decoding circuit and by estimating the most likelihood condition the data can take from among all changing conditions (i.e., the maximum likelihood sequence estimation) considering the trellis of convolutional code based on the received symbol S15, the received data S16 showing the data transmitted is restored and output. In this connection, FIG. 3B is a brief diagram showing the signal processing to be conducted in each circuit of the receiving device 10 explained above.
However, in the receiving device 10, the received data S16 is restored conducting the maximum likelihood sequence estimation by the Viterbi-decoding circuit 16. However, in order to restore the received data S16 with higher accuracy it is desirous to further improve the efficiency of the maximum likelihood sequence estimation.
This point will be described more specifically in the following paragraphs. The received symbol S13 to be supplied from the DQPSK demodulation circuit 13 is multi-level signal as described above. The value of this multi-level signal roughly shows the reliability of the received symbol. The Viterbi decoding circuit to decode such multi-level signal is generally called as a soft-decision Viterbi decoding circuit and in general, it restores data by conducting the maximum likelihood sequence estimation upon adding the reliability of each symbol. On the other hand, the Viterbi decoding circuit to decode the binary value signal having the value xe2x80x9cxe2x88x921xe2x80x9d or xe2x80x9c+1xe2x80x9d is generally known as a hard-decision Viterbi decoding circuit. When comparing this hard-decision Viterbi decoding circuit with the soft-decision Viterbi decoding circuit, it is generally said that the soft-decision Viterbi decoding circuit can conduct the maximum likelihood sequence estimation with higher accuracy than the hard-decision Viterbi decoding circuit. The reason is that in the case of soft decision Viterbi decoding circuit, since multi-level signal reflecting the reliability has been input, the estimation reflecting the reliability can be conducted. Accordingly, in order to increase accuracy in the maximum likelihood sequence estimation, it is considered that it would be better if the reliability of symbol were reflected by the signal to be input into the Viterbi decoding circuit.
However, in the case of TDMA system, the received symbol is transmitted after being divided into slots respectively, and it has a possibility that quality of communication varies on a slot-by-slot basis. Accordingly, in that case, it is considered that the maximum likelihood sequence estimation of the Viterbi decoding circuit can be done with higher precision if the reliability showing the communication quality of slot is reflected by the value of said symbol transmitted by that slot. Especially, when interleaves are conducted over multi-slots, it is possible that an erroneous estimation would be conducted if not reflecting the reliability because the reliabilities vary extremely by slot.
In view of the foregoing, an object of this invention is to provide a receiving device and a signal receiving method capable of decoding the data transmitted more accurately by conducting the high precision maximum likelihood sequence estimation.
The foregoing object and other objects of the invention have been achieved by the provision of a receiving method for receiving a signal composed of a set of predetermined information units. The receiving method comprises the steps of receiving the signal; calculating a weight coefficient showing the reliability of the received signal for each predetermined information unit; weighting the received signal by the weight coefficient; and decoding the weighted signal.
Further, according to this invention, a receiving device for receiving a signal composed of a set of predetermined information units, comprises: receiving means for receiving the signal; weight coefficient calculating means for calculating a weight coefficient showing the reliability of the signal output from the receiving means for each predetermined information unit; weighting means for weighting the signal output from the receiving means by the weight coefficient; and decoding means for decoding the signal output from the weighting means.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.